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Publication numberUS3322939 A
Publication typeGrant
Publication dateMay 30, 1967
Filing dateApr 8, 1963
Priority dateApr 13, 1962
Also published asDE1406390A1
Publication numberUS 3322939 A, US 3322939A, US-A-3322939, US3322939 A, US3322939A
InventorsCurties Maurice Cecil, John Oliver Beauchamp St
Original AssigneeFerranti Ltd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Flight aid system for indicating failure of the stabilizing system
US 3322939 A
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Description  (OCR text may contain errors)

May 30, 1967 Filed April 8, 1963 P/UK- arr M. C. CURTIES ET AL FLIGHT AID SYSTEM FOR INDICATING FAILURE OF HE STABILIZING SYSTEM 3 Sheets-Sheet l 40mm BIL/Z54 AU7'0S7746/L lZfQ tom/20m? DISPLA Y 9 smoky max/r ---49 0mm T09 COMP/17f? I nvenlom CURT 1135 o ,B'. ST. JOHN A Home yJ May 30, 1967 c R-n55 ET AL 3,322,939

FLIGHT AID SYSTEM FOR INDICATING FAILURE OF THE STABILIZING SYSTEM vFiled April 8, 1963 3 Sheets-Sheet 2 PAC/6 or;

MLC. CURTIES 0.15. ST. JOHN tlorn e y:

United States Patent 3,322,939 FLIGHT AID SYSTEM FOR INDECATTNG FATLURE OF THE STABILIZIPJG SYSTEM Maurice Cecil Curries, Light-water, and Oiiver Beauchamp St. John, Farnborough, England; said Curries assignor to Ferranti Limited, Hollinwood, Lancashire, England, a company of Great Britain and Northern Ireland Filed Apr. 8, 1963, Ser. No. 271,395 Claims priority, application Great Britain, Apr. 13, 1962, 14,300/ 62 Claims. (Cl. 235-1562) This invention relates to flight aid systems.

More specifically the invention relates to flight aid systems of the kind including a limited authority servo system, usually known as an autostabilizer, connected in series with a control input and operating in response to signals from an autostabilizer computer to provide artificial stability to a craft. Hereinafter such flight aid systems are referred to as flight aid systems of the kind specified. The invention is particularly, although not specifically, suitable for use in craft having one or more phases of unstable flight, for example helicopters and aircraft designed for vertical take-off and landing or short take-off and landing.

The control input in flight aid systems of the kind specified may be provided by a pilot operating a control stick in accordance With computed information displayed on a flight director display. Alternatively, the control input may be provided by an autopilot controlled by computed signals and acting in parallel with the pilots control stick. In both cases the computer supplying the information to the flight director or to the autopilot is designed to operate on the assumption that the craft to be controlled is maintained stable by the autostabilizer. In the event of a failure of the autostabilizer, however, the craft may become unstable With the result that the control demanded by the flight director or the control provided by the autopilot is no longer suitable for maintaining the craft in a desired state. If the craft is one having an unstable phase of flight and failure of the autostabilizer occurs during this phase the means available to the pilot for detecting and correcting the failure may not be adequate to maintain proper control of the craft.

It is an object of the present invention to provide a flight aid system of the kind specified in which compensation is provided in the event of failure of the autostabilizer.

According to the present invention a flight aid system includes a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, a flight director display, a flight director computer for controlling said flight director display, said flight director computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to its flight path error functions, and feedback means for applying to said flight director computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said flight director computer.

Also in accordance with the present invention a flight aid system includes a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, an autopilot, an autopilot computer for controlling the operation of said autopilot, said autopilot computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to its flight path error function, and feedback means for applying to said autopilot computer during correct operation of said 3,322,939 Patented May 30, 1967 autostabilizer a negative feedback for cancelling the stabilizing information from the output of said autopilot computer.

The present invention further comprises a flight aid system including a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, a flight director display, a flight director computer for controlling the operation of said flight director display, an autopilot, an autopilot computer for controlling the operation of said autopilot, said flight director computer and said autopilot computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to their flight path error functions, and feedback means for applying to said flight director computer and to said autopilot computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said flight director computer and from the output of said autopilot computer.

The present invention will now be described by Way of example with reference to the accompanying drawings in which:

FIGURES 1, 2 and 3 show schematic diagrams of different flight aid systems in accordance with the invention.

Referring now to FIGURE 1 of the drawings the flight aid system shown includes a pilots control stick 1 pivoted to the aircraft structure 2 and connected to a control rod 3, a spring feel 4 being connected to the bottom end of the stick 1. A limited authority autostabilizer 5 is connected in series with the control rod 3 and actuates an output control rod 6 connected to a member to be controlled.

The autostabilizer 5 is controlled by output signals from an autostabilizer computer 7, the signals being applied to the autostabilizer through an amplifier 8. The input to the autostabilizer compute-r 7 is derived from sensors 9, such as gyros, in Well known manner and negative feedback is applied to the computer 7 via the path 19 in accordance with the output from the autostabilizer 5.

The system also includes a flight director display 11 controlled by output signals from a flight director computer 12, the signals being applied to the flight director display 11 through an amplifier 13. The input to the flight director computer is derived from sensors 14 such as gyros or other devices and from inputs relating to the desired flight path which the craft is required to follow. The output of the flight director computer 12 is also controlled by means of negative feedback derived from a pick-oft" 15 which is responsive to the total movement of the output control rod 6 actuated by both the pilots cont-r01 stick 1 and the autostabilizer 5. The flight director 12 is designed to incorporate stabilizing control equations similar, but not necessarily identical, to those of the autostabilizer computer 7 in addition to its flight path error functions.

In operation, similar stabilizing information is supplied to both the autostabilizer computer 7 and the flight director computer 12. During satisfactory operation of the autostabilizer 5, however, the pick-off 15 senses the correction movements applied to the control rod 6 and the resulting negative feedback applied to the flight director computer 12 therefore cancels the stabilizing information computed in that computer. The only information appearing on the flight director display 11, therefore, is that relating to the long term control required to maintain the craft on a desired flight path.

In the event of a failure of the autostabilizer 5, however, the pick-off 15 will no longer provide a negative eedback to cancel the stabilizing information computed 1 the flight director computer. The required stabilizing nformation will therefore immediately appear on the .ight director 11 and the pilot, without any knowledge of he failure of the autostabilizer 5, will immediately start apply the necessary correcting control in response to he demands appearing on the flight director display 11. The pilot will, of course, soon be made aware of the ailure of the autostabilizer 5 by the changed nature of he demands appearing on the flight director display 11, he important point being that the pilot has retained conrol of the craft during the period between failure of the vutostabilizer 5 and the pilots recognition of this fact.

Referring now to FIGURE 2 of the drawings there is hown a flight aid system similar to that shown in FIG- J'RE 1 and like parts have therefore been given like refrence numerals. In this system, however, the flight direcor has been replaced by an autopilot 16 controlled by vutput signals from an autopilot computer 17, the signals teing applied to the autopilot 16 through an amplifier 18. The input to the autopilot computer 17 is derived from ensors 19 such as gyros or other devices and from inputs elating to the desired flight path which the craft is reuired to follow. The output of the autopilot computer .7 is also controlled by means of negative feedback deived from the pick-off and the computer 17 is also lesigned to incorporate stabilizing control equations simiar to those of the autostabilizer computer 7 in addition to ts flight path error functions.

The system operates in a manner similar to the system lescribed with reference to FIGURE 1, the stabilizing nformation being cancelled in the autopilot computer 17 luring normal operation of the autostabilizer 5. In the :vent of a failure of the autostabilizer 5, however, the tutopilot 16 is immediately supplied with stabilizing sigials. In practice it is likely that the autopilot 16 will have t slower servo response than the autostablizer 5 and if the :ontrol movement rates required to stabilize the craft are excessive the autopilot 16 may not be able to apply the ull correction necessary to stabilize the craft. Sufficient :ontrol of the craft may, however, be maintained to entble the pilot to regain control of the craft.

Referring now to FIGURE 3 of the drawings there is ahown a flight aid system combining the two systems delCI'lbd above with reference to FIGURES 1 and 2 and .ike parts have again been given like reference numerals. in this system the pick-off 15 is designed to supply sepa- -ate negative feedback signals to the flight director computer 12 and the autopilot computer 17. The flight direc- ;or 11 and the autopilot 16 are operated in the same nanner as described above with reference to FIGURES l and 2 respectively. This system has the advantage that when the automatic pilot 16 is in use the demands shown )n the flight director display are restrained by the action 3f the autopilot 16 to small values around the zeros of :he displays. In the event of a failure in the autopilot chan- Jel or the flight director channel the movements of the light director indices Will increase. The indices of the Flight director may therefore be fitted with suitable contact or other detection devices to indicate movement beyond a normal limit, this indication being used to signify a fault condition. Furthermore, if in such a system the flight director computer 12 is used to control two flight directors through two separate amplifiers the contacts or other detection devices in each flight director may be :onnected in series and the two contact chains thus formed may be connected in parallel so that a failure of one director and its amplifier may be isolated from the more serious event of a failure of the sensors or computer in either the flight director or the autopilot.

Each of the systems described above may be modified by the inclusion of a wash-out network in the feedback path from the pick-off 15 to the flight director computer 12 and/or the autopilot computer 17. By the expression wash-out is meant a network which gives zero output during steady state conditions but which responds to transient short term disturbances. The inclusion of such a network ensures that any steady output from the pick-off 15 as a result of failure of the autostabilizer 5 is not applied as a false bias to the flight director computer 12 or the autopilot computer 17. The transient outputs from the pick-oif 15 due to movements of the control rod 6, however, remain unaffected.

Although the feedback applied to the flight director computer and/or the autopilot computer has been described above as being derived from a single pick-off 15 on the output control rod 6, the feedback may be derived by combining a feedback signal representing the control movements of the autostabilizer with a feedback signal representing the pilots or the autopilots control movements which may be derived from a pick-ofl on the control rod 3.

What we claim is:

1. A flight aid system for an aircraft having a member to be controlled while the aircraft is in flight including a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, an output control member operatively connected to the member to be controlled and actuated by said autostabilizer, a flight director display, a flight director computer for controlling said flight director display, said flight director computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to its flight path error functions, and feedback means responsive to the movement of said output control member for applying to said flight director computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said flight director computer.

2. A flight aid system as claimed in claim 1 including a pilot-operated control member connected in series with said autostabilizer, and wherein said feedback means comprises pick-off means responsive to the movement of said output control member, said movement being the total of the autostabilizer and the pilot-operated control movements, the output of said pick-off means being fed back to said flight director computer.

3. A flight aid system for an aircraft having a member to be controlled while the aircraft is in flight including a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, an autopilot, an autopilot computer for controlling the operation of said autopilot, said autopilot computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in additon to its flight path error functions, an output control member connected to the member to be controlled and actuated by both said autostabilizer and said autopilot, and feedback means responsive to the total movement of said output control member for applying to said autopilot computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said autopilot computer.

4. A flight aid system as claimed in claim 3 in which said feedback means comprises pick-01f means responsive to the total movement of said output control member,

the output of said pick-oft means being fed back to said autopilot computer.

5. A flight aid system for an aircraft having a member to be controlled while the aircraft is in flight including a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, a flight director display, a flight director computer for controlling the operation of said flight director display, an autopilot, an autopilot computer for controlling the operation of said autopilot, said flight director computer and said autopilot computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to their flight path error functions, an output control member operatively connected to the member to be controlled and actuated by both said autopilot and said autostabilizer, and feedback means responsive to the total movement of said output control member for applying to said flight director computer and to said autopilot computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said flight director computer and from the output of said autopilot computer.

6. A flight aid system as claimed in claim 5 including a pilot-operated control member connected to said output control member, and wherein said feedback means comprises pick-off means responsive to the movement of said output control member, said movements being the total of the autostabilizer movements and the movements of said pilot operated control member and said autopilot, the output of said pick-otf means being fed back to said flight director computer and said autopilot computer.

7. A flight aid system as claimed in claim 5 in which said flight director display includes flight director indices, and means for indicating movements of the flight director indices beyond a predetermined limit.

8. A flight aid system for an aircraft having a member to be controlled while the aircraft is in flight comprising a limited authority autostabilizer, an autostabilizer computer for controlling the operation of said autostabilizer, a control computer designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to flight path error functions, a control member adapted to be acted upon in response to the output of said control computer and connected in series with said autostabilizer, an output control member operatively connected to the member to be controlled and actuated by both said control member and said autostabilizer, and feedback means responsive to the total movement of said output control member for applying to said control computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the output of said control computer.

9. A flight aid system as claimed in claim 8 in which said feedback means includes a Wash-out network which gives zero output during steady state conditions but which responds to transient short term disturbances.

10. A flight aid system for an aircraft having a member to be controlled while the aircraft is in flight comprising a control rod operatively connected to the member to be controlled, a limited authority autostabilizer connected in series with said control rod, an autostabilizer computer having an input connected to said autostabilizer for controlling the operation of said autostabilizer, a flight director for providing to the pilot of the aircraft a visual display of computed flight information, a flight director computer having an output connected to said flight director for controlling the operation of said flight director, a control stick manually operable by the pilot of the aircraft connected to said control rod and adapted to be positioned in accordance with said visually displayed computed flight information, an autopilot, an autopilot computer having an output connected to said autopilot for controlling the operation of said autopilot, said flight director computer and said autopilot computer being designed to incorporate stabilizing control equations similar to those of said autostabilizer computer in addition to flight path error functions, means connecting the output of said autopilot to said control rod, whereby said control rod is actuated by both said autopilot and said autostabilizer and by said control stick, and feedback means for applying to said flight director computer and to said autopilot computer during correct operation of said autostabilizer a negative feedback for cancelling the stabilizing information from the outputs of said flight director computer and said autopilot computer, said feedback means comprising pick-off means responsive to the total movement of said control rod, the output of said pick-off means being fed back to both said flight director computer and said autopilot computer.

References Cited UNITED STATES PATENTS 2,548,278 4/ 1951 Wirkler. 2,751,541 6/1956 Schuck 235150.2 X 2,869,804 1/1959 Muinch et al. 235-150.2 X 2,996,268 8/1961 Broun et a1. 235150.25 X 3,221,230 11/1965 Osburn.

FOREIGN PATENTS 815,137 6/1959 Great Britain.

MALCOLM A. MORRISON, Primary Examiner.

l. KESCHNER, Assistant Examiner.

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US2548278 *Aug 17, 1949Apr 10, 1951Collins Radio CoAircraft course stabilizing means
US2751541 *Jan 16, 1952Jun 19, 1956Honeywell Regulator CoAutomatic flight control apparatus
US2869804 *Jul 26, 1955Jan 20, 1959Hughes Aircraft CoAcceleration responsive control surface control limiting system for aircraft
US2996268 *Nov 25, 1957Aug 15, 1961Gen Motors CorpInertial guidance system
US3221230 *Jan 22, 1962Nov 30, 1965Massachusetts Inst TechnologyAdaptive control method and apparatus for applying same
GB815137A * Title not available
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US3474407 *Aug 6, 1965Oct 21, 1969Elliott Brothers London LtdApproach and landing signalling systems for aircraft
US3570788 *Jan 31, 1969Mar 16, 1971Ferranti LtdFlight aid systems
US3676843 *Apr 27, 1970Jul 11, 1972Bodenseewerk Gergtetechnik GmbDirectional and pitch trim indicator for automatic pilots
US4109886 *Jan 12, 1976Aug 29, 1978Sperry Rand CorporationSemi-automatic flight control system utilizing limited authority stabilization system
US6142416 *Mar 14, 1997Nov 7, 2000General Electric CompanyHydraulic failsafe system and method for an axisymmetric vectoring nozzle
Classifications
U.S. Classification701/3, 340/963, 701/11, 244/194, 700/71
International ClassificationB64C13/24, B64C1/00, G05D1/08, B64C27/82
Cooperative ClassificationB64C13/24, B64C2700/6229, B64C27/82, G05D1/0833
European ClassificationB64C13/24, G05D1/08B2C, B64C27/82